1. Field of the Invention
This invention relates to the etching of silicon, and, more particularly, to the improved anisotropic etching of single crystal silicon.
2. Description of the Prior Art
The anisotropic etching of single crystal silicon has been carried out for many years in the production of microelectronic devices. An essential feature is that the etching solution etch the (100) crystallographic plane at an appreciably greater rate than the (110) and (111) planes, producing v-shaped sidewalls at 54.74.degree. from the (100) surface. Exemplificative of the solutions which are known in the art are the following: IBM Tech. Discl. Bull., Vol. 19, No. 9 (February 1977), p. 3623 discloses a solution for anisotropically etching single crystal silicon, containing ethylene diamine, pyrocatechol and water; and IBM Tech. Discl. Bull., Vol. 19, No. 10 (March 1977), p. 3953 also describes such a solution, containing the three ingredients described in the preceding article, but further including hydrogen peroxide.
See also, U.S. Pat. Nos. 4,417,946, issued to Bohlen et al on Nov. 29, 1983, and 4,342,817, issued to Bohlen et al on Aug. 3, 1982, both of which disclose a method of making a mask, employing an etching solution consisting of ethylene diamine, pyrocatechol, water, and, optionally, hydrogen peroxide; and U.S. Pat. Nos. 4,293,373, issued to Greenwood on Oct. 6, 1981, and 4,229,979, issued to Greenwood on Oct. 28, 1980, both of which disclose a method of making a silicon transducer which involves etching a boron doped silicon wafer, with a solution containing ethylene diamine, pyrocatechol and water.
Note also, U.S. Pat. No. 3,650,957, issued to Shipley, Jr. et al on Mar. 21, 1972, which discloses a solution for etching copper, which includes a source of cupric ions, a complexing agent for cupric ions, such as a hydroxy-carboxylic acid or an alkanolamine, a source of chloride or bromide ions and a solution soluble molybdenum, tungsten or vanadium compound.
U.S. Pat. No. 3,873,203, issued to Stevenson on Mar. 25, 1975, discloses a mixture for etching silicon, containing hydrazine and pyrocatechol.
Further, U.S. Pat. No. 3,160,539, issued to Hall et al on Dec. 8, 1964, relates to an etching solution for silicon, which includes piperidine.
IBM Tech. Discl. Bull., Vol. 15, No. 1 (June 1972), p. 173 discloses an etchant for aluminum, consisting of a solution of a secondary organic amine, such as piperidine or pyrrolidine, in water.
In addition, a particularly effective solution for etching single crystal silicon is disclosed in U.S. patent application Ser. No. 875,833, filed by Beechko on June 18, 1986. That solution comprises ethanolamine, pyrocatechol, water, hydrogen peroxide and piperidine. It has been found that the solution etches (100) silicon at a rate of about 40 .mu./hr.